This is an interesting thread. I am a 7 cap that has used stiff shafts since my 20's, getting a new set of Mizuno irons every 2-3 years. This past week, I played with a customer in NJ with a rental set of Speedblade irons. I shot a 74 in a harsh wind & it wasn't until after the round I looked down at the clubs to take a picture that I noticed that the shafts were Regular.
Now I'm confused, not knowing if I striped everything because I was just on that day moreso than normal, I was using R shafts or the Taylormade irons just suit me better....